Lecture 13 Overview of Earth’s History

Hadean (4.5 to 3.9 b.y.)1. Initial Formation of the Earth

2. Impact of Mars-sized planet- Formation of Moon

3. Era of Asteriodal Bombardment (4.1 to 4.5 b.y.)- The evidence?

Archean (3.9 to 2.5 b.y)1. Formation of First Stable Crust

2. The Archean Atmosphere

3. The Origins of Life- Oldest Fossil - 3.5 b.y.

What was the Archean world like?

Stromatolite

Primitive UnicellularOrganisms

Proterozoic (0.54 to 2.5 b.y.) 1. Compare Archean and Proterozoic Sedimentary Rocks

- The Early Proterozoic is the first period of large-scale stability (2.5 b.y)

2. The Biggest Pollution Event of the Earth- At about 2.2 to 2.0 by sediment deposited on land develops a red color. Before that only oceans sedimentwas red

3. The presence of oxygen supported the developmentof more complex organisms (1.2 b.y)

Eukaryotes versus prokaryotes

4. Snowball Earth (600 to 700 m.y.)- Strange Climatic Conditions- The Entire Earth Froze-up

5. The Origin of Animals (≈ 600 m.y.)- First Animals Lack Durable Hard Parts

- Fossil Evidence is Indirect- Called Trace Fossils

Paleozoic (250 to 540 m.y.)- Early Paleozoic (420 to 540 m.y.)

1. Origin of Animals with Skeletal Hard Parts

During the Early Paleozoic a rich diversity of sea life existed

Q: What is missing in this photo?

2. The continents are not fixed. They move - But,very slowly

Late Paleozoic (250 to 420 m.y.)3. Origin of Terrestrial Life

Toward the end of the Paleozoiclarge forests consisting of ferntrees were established

-These swampy forests ultimatelygenerated most of the world’s coal

Also during the Late Paleozoic land animals evolved

InsectsAmphibiansReptiles

4. Also toward the end of the Late Paleozoic all of the continents wereassembled to form thesupercontinent Pangaea

Gradual movement of continents over geologic time is calledcontinental drift.

5. Permian Extinction

Mesozoic (66 to 250 m.y.)1. Break-up of Pangaea

- The result: Formation of the Atlantic Ocean

2. In terms of life this era is known as the Age of the Dinosaurs

3. During the Mesozoic other lifeforms developed

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4. What happened at the end of the Mesozoic??

What caused the extinction of the dinosaurs?

The big one?

Where did this asteroid impact?

Cenozoic (0 to 66 m.y.)

1. Global Cenozoic Plate Tectonics- The Mesozoic was a period in which continents were in general moving away from one another

- Exception: collision of India with Eurasia

2. The Mediterranean Basin about 6 to 7 m.y. ago

3. Cenozoic LifeMammals and flowering plants become dominant

4. The Quaternary “Ice Age” (0 to 2 m.y.)- Climate variability is the norm

Glacial versus interglacial periods

- The Quaternary glacial periods has it roots in thedevelopment of ice sheets at south pole over 30 m.y.

- In summary when looking at earth’s history as a whole ice sheets are rare even at the poles except during the last 30 m.y.